The invention relates generally to devices for providing a secure, engageable lip on the edge of sheet material and more specifically to a lead edge strip for securement to a printing plate carrier sheet which includes a lip complementary to and engageable with an overhanging edge on a printing cylinder.
Flexographic printing, also known as flexography or aniline printing, is a generally preferred printing process for large areas such as containers and cardboard cartons, point of purchase displays and the like. Flexographic printing is relief, i.e., direct, printing utilizing large plates fastened to a rotating cylinder. It is capable of producing an image with exceptional clarity and contrast. A single inking roller supplied with aniline ink from rollers in the ink fountain provides ink to raised, image forming printing plates disposed on the rotating cylinder which print directly upon the product. The carrier sheet or mounting material which carries the printing plate or plates may be several inches on each side or several feet. The carrier sheet is mounted to the printing plate cylinder at one edge by cooperation between a lip on the lead edge of the carrier sheet and a complementarily configured channel and undercut lip on the cylinder. The opposite edge of the carrier sheet is secured to the plate cylinder by one, or typically a plurality of, elastic straps which retain the carrier sheet upon the plate cylinder and properly tension it.
Since the elastic mounting straps merely provide tension to the carrier sheet to retain it upon the printing plate cylinder, it is apparent that the location and the registration of the carrier sheet and thus of the print plate disposed thereon is almost exclusively the result of cooperation between the leading edge strip of the carrier sheet and the complementary lip on the printing plate cylinder. Since the printing plate cylinder is most generally fabricated of metal, it may be considered dimensionally stable and may thus be virtually ruled out as a source of variability and error when installing and utilizing flexographic printing plates. However, since the carrier sheet and its mounting edge are relatively lightweight, correct mounting and stability are concerns with regard to same. Accordingly, significant attention has been directed to the mounting method and configuration of carrier sheets and mounting edge.